The present invention is directed to devices and methods for correcting atmospheric induced faults in a radio signal, and more particularly to a device and method for correcting an amplitude slope in a frequency domain of a digital radio signal.
Digital radios may operate in frequency bands that exceed 2 GHz. Most propagation conditions have little or no affect on the transmission of digital signals in this frequency band, but certain meteorological conditions, notably some temperature and humidity combinations, may produce multipath interference or reflective fading.
Multipath interference may cause a slope asymmetry in the frequency domain of the digital radio signal. For example, as shown in FIG. 1, the amplitude of the radio signal may vary in the frequency domain between lower frequency limit f1 and upper frequency limit f2 causing the amplitude to have a slope .alpha.. The desired amplitude slope is indicated by the dashed line.
As is known, the amplitude slope may be corrected by applying a slope correction to the radio signal. For example, signal amplitude at f1 and f2 may be sensed in filters set to f1 and f2. The sensed amplitude information may be used to control the Q of out-of-band low and high frequency filters, thereby adjusting the amplitude slope of the signal. However, the slope detection mechanism and subsequent adjustment may also change the amplitude of the output, and a further sensor for the amplitude of a mid-range frequency and a gain control mechanism for adjusting amplitude are needed. The further sensor and gain control mechanism increase complexity and cost of slope correction devices. Further, adjustment of the values of f1 and f2 is not convenient as new filters are required. See, for example, the device in U.S. Pat. No. 4,245,353 issued Jan. 13, 1981 to Bynum.
Accordingly, it is an object of the present invention to provide a novel device and method for correcting an amplitude slope in the frequency domain of a radio signal that is less complex and less costly than prior art devices, thereby obviating the problems of the prior art.
It is another object of the present invention to provide a novel device and method for correcting an amplitude slope in the frequency domain of an input signal in which a slope is detected using mixers in parallel feedback loops connecting an output signal to inputs to out-of-band high and low frequency notch filters, where each of the mixers combines the output signal with one of the high and low frequencies that define the frequency domain.
It is yet another object of the present invention to provide a novel device and method for correcting an amplitude slope in the frequency domain of an input signal in which parallel feedback loops each downconvert an output signal to a frequency that is an upper or lower limit of the signal frequency domain, and the energy in the downconverted signal is provided as a slope correction signal to one of parallel notch filters.
It is still another object of the present invention to provide a novel device and method for correcting an amplitude slope in the frequency domain of an input signal in which parallel feedback loops each downconvert an output signal to a frequency that is an upper or lower limit of the signal frequency domain, and in which the energy in the downconverted signal is sensed in a low pass filter which harnesses the energy and provides it as a slope correction to change the Q of parallel notch filters from which the output signal is provided.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.